Craniomandibular osteopathy ("lion jaw")

What is ... ?: 

 In this disease, there is excessive, abnormal bone growth on the skull (cranium) and lower jaw (mandible). Extra bone grows on the surface of the lower jaw, making it wider and thicker. It may also affect the jaw joint (temporomandibular joint). In severe cases, the excess bone may prevent the jaw joint from opening and closing normally. Abnormal bone growth will typically stop and begin to regress by one year of age.

How is ... inherited?: 

The mode of inheritance is autosomal recessive in West Highland white terriers. In other breeds, the mode of inheritance has not been determined.

What does ... mean to your dog & you?: 

 Your puppy (3-8 months of age) may have a swollen and painful lower law, or have trouble opening the mouth or eating, or drool excessively. You may not notice all of these problems continuously; the signs may seem to flare up at times then get better. This disease is "self-limiting." After your puppy reaches one year of age, the condition will probably not get worse, and should get better. However if there has been severe bone growth, especially involving the jaw joint, the excess bone may not go away on its own. In some cases, particularly if the jaw joint is not working properly, your dog may need surgery. Your puppy’s condition is more serious and the prognosis is guarded if there is excessive bone growth on the base of the skull.

How is ... diagnosed?: 

 Your veterinarian will diagnose this disease based on physical examination, history, and x-rays.

How is ... treated?: 

 There is no treatment to stop the disease from getting worse; it will usually get better as your puppy grows up. Pain can be treated with anti-inflammatory drugs. Your puppy may need surgery in certain severe cases.

For the veterinarian:  Bony proliferation is usually bilateral. Clinical signs of this disease (including swollen mandible which may be painful, and difficulty or pain opening the mouth), may be intermittent, and may be associated with pyrexia. Radiographs may show involvement of bones of the skull other than the mandible and temporomandibular region. In some cases, bone biopsy and histopathology may be helpful in differentiating this disease from other conditions involving excess bone growth. This disease is self-limiting, and excess bone should not proliferate beyond one year of age. Excess bone may not completely regress. Pain may be managed with anti-inflammatory drugs.

Breeding advice: 

 Affected dogs should not be used for breeding, even if they appear to recover completely. Breeding of parents (carriers) and siblings (suspect carriers) should also be avoided. The Institute for Genetic Disease Control in Animals (GDC)   and the Orthopedic Foundation for Animals (OFA) maintain registries for this condition in terrier breeds.



 Johnson, KA, Watson, ADJ, Page, RL. 1995. Skeletal disease. In EJ Ettinger and EC Feldman(eds.) Textbook of Veterinary Internal Medicine, p. 2077-2103.   W.B. Saunders Co., Toronto.

 Institute for Genetic Disease Control in Animals -

Orthopedic Foundation for Animals -

What breeds are affected by ... ?